1. Field of the Invention
The present invention relates to a semiconductor device such as a Schottky barrier diode using a silicon carbide semiconductor substrate and a method of manufacturing the same.
2. Description of Related Art
The configuration of a Schottky barrier diode using a silicon carbide (SiC) semiconductor substrate is as shown in FIG. 9(e). One surface of a SiC semiconductor substrate 100 is a silicon surface 110, and the other surface thereof is a carbon surface 120. A SiC epitaxial layer 101 is formed on the side of the silicon surface 110.
A titanium (Ti) metal layer 30, for example, is formed on the silicon surface 110, and a Schottky junction is formed in an interface between the silicon surface 110 and the Ti metal layer 30. Further, an Al surface electrode 50, for example, is formed on a surface of the Ti metal layer 30 in order to ensure good adhesion to a metal wire composed of aluminum (Al) or the like, for example, for making connection to an external electrode.
On the other hand, a nickel (Ni) metal layer 20, for example, is formed on the carbon surface 120, and an ohmic junction is formed in an interface between the carbon surface 120 and the Ni metal layer 20. Further, in order to satisfactorily connect the Schottky barrier diode to an external substrate having copper (Cu) wiring, for example, a silver (Ag) reverse surface electrode 40, for example, is formed on a surface of the Ni metal layer 20.
In manufacturing the Schottky barrier diode, the Ni metal layer 20 is formed on the carbon surface 120 of the SiC semiconductor substrate 100 having the epitaxial layer 101 on the side of the silicon surface 110 (step Ti in FIG. 10). In order to form a good ohmic junction in the interface between the carbon surface 120 and the Ni metal layer 20, the Ni metal layer 20 is heat-treated at 1000° C. for twenty minutes (step T2).
As shown in FIG. 9(b), the Ti metal layer 30 is formed on the silicon surface 110 of the SiC semiconductor substrate 100 (step T3 in FIG. 10). Thereafter, a resist 60 is applied to the surface of the Ti metal layer 30 to pattern the Ti metal layer 30 (step T4), as shown in FIG. 9(c), after which the Ti metal layer 30 is subjected to etching processing (step T5 in FIG. 10).
After the resist 60 is removed, the Ti metal layer 30 is heat-treated at 400° C. for twenty minutes, as shown in FIG. 9(d), in order to form a good Schottky junction to the SiC semiconductor substrate 100 (step T6 in FIG. 10). Thereafter, the Al surface electrode 50 and the Ag reverse surface electrode 40 are respectively formed on the surfaces of the Ti metal layer 30 and the Ni metal layer 20 (step T7), thereby forming the Schottky barrier diode shown in FIG. 9(e).
As described in the foregoing, the Ni metal layer 20 and the Ti metal layer 30 are individually formed during manufacturing processes (steps Ti and T3), and are individually heat-treated (steps T2 and T6). Therefore, the heat treatment must be carried out at least twice, thereby making it difficult to shorten the manufacturing processes.
Furthermore, the Ni metal layer 20 is used as an ohmic electrode. Unless the heat treatment is carried out at a high temperature of approximately 1000° C., as shown in the step T2 in FIG. 10, therefore, a good ohmic junction cannot be formed in the interface between the Ni metal layer 20 and the carbon surface 120 of the SiC semiconductor substrate 100. Therefore, the operating characteristics of the Schottky barrier diode may be adversely affected by the heat treatment during the manufacturing processes, resulting in poor manufacturing yields.